I also looked at OneCnc but already have my money invested in Visualmill 4.0 and am getting ready to upgrade to 5.0. As a hobbiest, I just can't afford to start from scratch and lose my investment in Visualmill.
The VM 5.0 upgrade certainly is a Major upgrade and thats the route I am going to take. However if I were starting with nothing, I would certainly consider OneCNC as a front runner for my money.
Alan T.